1. Field of the Invention
The present invention relates to a fluid fuel heater, particularly a liquid fuel heater, to heat air and to introduce it into an environment to be heated. Particularly, it is a movable heater particularly having a high heating power, for example, with a cart, suitable to be easily transported and temporarily placed in different working places, sometimes at environmental and atmospheric conditions even very different from one another, for example in a construction site at a high height or even at sea level, in a mine, in an industrial warehouse. According to another aspect, the invention relates to a method to operate such heater.
2. Description of the Related Art
Environmental air fuel heaters are known, which are suitable to generate a hot air flow by the combustion of a fuel and to introduce the heated air into the environment. Sometimes such heaters have a high heating power and produce a considerable flow of hot air. Furthermore, sometimes such known heaters are mounted on a wheeled cart, and the cart can be dragged by a transport means.
A known heater of this type comprises a tubular combustion chamber, generally arranged with a horizontal axis, a liquid fuel supply duct that ends with a nebulizer nozzle, suitable to nebulize the fuel in the combustion chamber, and a forced ventilation device that inputs oxidizing air into the combustion chamber in which the nebulized fuel is dispensed. The combustion is initiated by an ignition device which generates sparkles.
As it is known, the combustion process, in order to take place in an optimal manner, has to be carried out according to a suitable stoichiometric ratio between fuel amount and air amount, i.e., the nebulized fuel and the air have to result in a stoichiometric mixture, i.e., according to a wee-determined stoichiometric ratio.
When the amount of one of the two components of the mixture varies with respect to the amount of the other one, with reference to the stoichiometric ratio, the combustion quality is affected thereby.
For example, if the air amount is less than that provided for in the stoichiometric ratio, the combustion can be incomplete and originate an efficiency loss of the combustion with emission of fumes of non-combusted carbon, generally having a characteristic black appearance. Under certain conditions, fumes with high Bacharach levels can be generated.
In other situations, if the amount of oxidizing air falls below a predetermined threshold with respect to the fuel amount, it can happen that the combustion does not even start.
Therefore, the known heaters of this type have a drawback of having a combustion and operation quality that is strongly affected by the atmospheric conditions, and particularly by the air density.
Particularly, a known heater of this type, which is adjusted for an optimal operation at the sea level, if is transported at a high altitude, for example to heat an industrial warehouse or a construction site at 4000 meters above the sea level, will undoubtedly produce a high amount of fumes, or it will not even able to start the combustion due to the reasons explained above, due to the decrease of the air density.
Sometimes, the known heaters provide for a mantle which externally wraps the combustion chamber forming an interspace in which an environmental cooling air flow is introduced, which cools the combustion chamber and concomitantly heats by contact therewith, to then exit the heater, thus heating the environment.
The decrease of the air density when the heater, adjusted in order to operate in an optimal manner at sea level, is brought to a high altitude, very adversely affects also the combustion chamber cooling efficiency by the air flow in the external interspace.
In fact, the lesser air density allows a less heat to be removed from the combustion chamber, therefore it produces at the same time an overheating of the combustion chamber and an overheating of the mantle. This drawback is unacceptable both because it can result in an irreversible damage of the heater, and because it is dangerous due to the risk of burns of a user who inadvertently touches the mantle.
Therefore the air density changing adversely affects not only the combustion quality per se, but also the heat subtraction from the cooling air.
In order to avoid this worsening of the combustion due to the increase in the temperature of the combustion chamber, a fuel flow rate reduction would be needed. The known liquid fuel heaters do not allow this flow rate decrease, since they use a nebulization nozzle, which nebulizes only above a predetermined nebulization pressure threshold of the pumped fuel, i.e., beyond a determined minimum fuel flow rate. In other terms, it is not possible to reduce the fuel flow rate below a minimum fuel flow rate, because no nebulization would occur below it.
A solution, which is anyhow disadvantageous, could be to replace the nozzle with another one having different characteristics, each time the air density changes.
However, replacing the nozzle with another one having different characteristics each time the heater is moved from a site to another one with different environmental characteristics, particularly with a less pervious nozzle to reduce the dispensed fuel amount, would involve the further drawback of requiring much working time, and especially qualified personnel. During the replacement operations, the heater should be turned off and this would involve a stop of the construction site operations.
On the contrary, the need is felt that such heaters are capable of operate in an optimal and reliable manner without the intervention of qualified personnel, since they are intended to operate under extreme environmental conditions, sometimes in places which are very far from inhabited sites or technical assistance centers.
Therefore, the need is felt to provide a movable, or transportable fluid fuel air heater that can be adapted to environmental conditions, particularly at altitudes and external temperatures that are very different from one another, in a quick and inexpensive manner and avoiding to require the intervention of qualified personnel.